Bioactive material

ABSTRACT

A process and apparatus for manufacture of biocide products are described. The biocide properties arise from the caustic calcined powder, from carbonates such as such as magnesite and dolomite, and from hydroxides such as brucite. The method of manufacture is based on the production of high surface area oxide particles using an indirectly heated counterflow reactors for specifically calcining the carbonates and the hydroxides without significant sintering. The biocide products may be a powder or a hydrated slurry. A hydrated slurry is preferred for agricultural applications as a spray. For aquaculture applications, the products have a preferred particle size distribution to impact the aquatic and benthic ecosystems, and a Ca/Mg ratio that promotes the growth of the cultivates species when applied as a powder or a slurry. For applications such as a marine paint, the powder product or the slurry product is mixed with various agents to form a setting coating, and is applied to the infrastructure that is otherwise subject to biofilm growth.

TECHNICAL FIELD

The present invention relates broadly to the production of a materialproduct that is a contact biocide for use in agriculture, aquacultureand other applications, and which is produced from calcined powdersusing flash calcination of materials. This invention is a furtherdevelopment of a generic bioactive material, and its method ofmanufacture, described by Sceats (AU2014374829) and Sceats and Hodgson(AU2015904534), included herein in their entireties, in which thegeneral method of manufacture described therein is further adapted forthe production of material by optimising the bio-activity, by extendingthe range of the materials that can be used to manufacture the productand thereby extending the range of applications of the product.

BACKGROUND

Sceats, and Sceats and Hodgson, focused on the application of theproduct to agriculture, but there is a broader range of potentialapplications. For example, in 2016, aquaculture farming production,especially for fish, mollusks and crustaceans, exceeded that from wildcapture commercial fishing. This transition has been driven by demandfrom growing human populations and the stagnation of wild capture. TheFood and Agriculture Organisation (FAO) of the United Nations hasreported that in 2015 the world aquaculture production reached 97.2million tonnes (live weight) with an estimated value of USD157 billionin 2013 with a growth rate of 5.6%. The FAO reports that its GlobalAquaculture Production statistics database shows that 575 aquaticspecies grown in freshwater, seawater and brackish water have beenregistered.

Intensive aquaculture farming practices are rapidly evolving, comparedto those of agriculture, which have evolved over thousands of years. Thevery high population density of the cultivated species in farmingcompared to the wild leads to the occurrence, severity and spread ofdiseases within and between aquaculture populations in ways that aresimilar to those associated with diseases in dense human and terrestrialanimal populations. Factors that impact on the development and severityof a disease following exposure of the cultivated species to a pathogeninclude the virulence of the pathogen, the immune, genetic andphysiological condition of the cultivated species; and its stress andpopulation density; as well as the general environmental conditions ofboth the aquatic and benthic ecosystems of an aquaculture pond or pen.The cultivated species population density is the most important factorin the spread of diseases in aquaculture, because of the increased rateof infection. This dense population in the aquatic environment, and thelimited water flow, facilitates the spread of pathogens, and the benthicenvironment is often a source of such pathogens. The development of adisease and the relevant severity of that disease within the cultivatedspecies population is influenced by a complex interaction of thesevariables associated with the pathogen, the cultivated species and thesetwo environments.

There is a third ecosystem in aquaculture systems, which is the pond orpen infrastructure that may comprise the wall structure of the pens, thebottom of boats, and equipment used to manage the farm such as feedersand boats. These surfaces are subject to the growth of biofilms, and theimpact of these films on this critical infrastructure has a significanteconomic impact. Biofilm growth suppression had previously beenprevented by the use of very toxic materials, such as tri-butyl tin.However, this material leached the toxic materials into the aqueousecosystems, and many such compounds have been subsequently banned inmost countries. Other systemic biocides have been deployed that have areduced impact but there are concerns about the potential for suchsystems to leach, as well as the growth of resistance. There is a needfor a non-toxic coating material of marine infrastructure such aswharves, piles, nets, ships and boats that can suppress the growth ofbiofilms, and in the context of aquaculture, this includes all thesurfaces of the aquaculture pens and systems. The ability of pathogensto move between the aquatic ecosystem, the benthic ecosystem and thisinfrastructure ecosystem means that all three ecosystems need to bemanaged in aquaculture.

The ecosystems in aquaculture comprise the aquatic, benthic andinfrastructure zones. The pathogen are may first incubate in the benthiczone and then progress to the aquatic zone, because the benthic zoneoften becomes polluted more quickly. In addition, systemic biocides areoften applied to the aquaculture systems just to prevent biofilmgeneration, and these can find their way into the aquatic and benthicecosystems. Therefore, aquaculture is therefore difficult to target withsystemic biocides. There is a search for materials that can mitigate thedevelopment and spread of diseases so that costly intervention withsystemic biocides is rarely required and prudently applied. Such amaterial would likely be a contact biocide to ensure that it is activeagainst a wide spectrum of diseases.

Just as for agriculture, there is a need for methods of infectiousdisease controls that preferably impacts positively against thepathogen, while benefiting the cultivated species and the environment.However, the same sets of issues arise in aquaculture as in agricultureand human health, whereby diseases in the cultivated species rapidlybecome tolerant to systemic biocides through adaptation. Such biocidesare generally neurotoxic compounds, which are toxic to both humans andanimals. In aquaculture, the use of such compounds is limited becausethe cost of chemicals generally exceeds the benefits. For a contactbiocide application in aquaculture, the contact requirement is met by amaterial that is largely insoluble, and an additional challenge wouldthen be to find a means of application in which contact can be made ineach of the aquatic, benthic and infrastructure ecosystems.

There has been an extensive development of nano-materials with biocideproperties, and in particular, of nano-magnesia MgO and nano-zinc oxideZnO. An example of a biocide is ‘Antibacterial characteristics ofmagnesium oxide powder_, J. Sawei et. al. World Journal of Microbiologyand Biotechnology, 16, Issue 2, pp 187-194 (2000) and T. Y in and Y. He,‘Antibacterial activities of magnesium oxide nanoparticles againstfoodborne pathogens_ J. Nanopart. Res. 13, 6877-6885. In the study bySawai et al, the objective was to make high surface area MgO withparticle sizes below about 50 nm. In trials of these materials, the MgOparticles rapidly react with water to form nano-magnesium hydroxideMg(OH)₂. Prior art references to nano-MgO are ascribed herein tonano-Mg(OH)₂. These hydrated nano-materials exhibit broad spectrumbioactivity response to viruses, bacteria and fungi. However, the costof production of nano-materials is such that they are rarely deployed inaquaculture. Furthermore, there are concerns about the toxicity ofnanomaterials in general because they are readily entrained in breathsof air, and fast diffusion through the skin.

The process for production development of nano-active Mg(OH)₂ fromcarbonate minerals such magnesite and dolomite has been described, forexample, by Sceats and Sceats and Hodgson. In that approach, Mg(OH)₂particles in the range of about 0.4-100 microns are produced which arecomposites of nano-scale crystallites in an aqueous solution. Tests ofthe effectiveness in agriculture have demonstrated that these materialshave the same bio-active responses to bacteria, fungi and viruses as theMg(OH)₂ nano-particles, and they are therefore deemed to be nano-active.The larger particles are in an aqueous solution, and are not entrainedin air for breathing, and the particles are too large to diffuse throughthe pores in the skin. The toxicity to humans is the same as largeMg(OH)₂ particles, as in Milk of Magnesia, but the material retains thenano-activity to pathogens through their nano-crystalline structure. Inthis invention, that approach to production is extended to the use ofbrucite as a source of MgO, with the brucite being either a mineral or asynthetic material produced from brine.

In agricultural applications, the bio-activity is generally realised bydiluting the slurry in water, and applying it to leaves of plants as afoliar spray. Without being bound by theory, the bio-activity observedin agricultural tests as a spray is ascribed to the release of ReactiveOxygen Species, such as peroxide and superoxide radicals that areproduced on the high energy edges of the MgO nano-crystallites that areformed during flash calcination of Magnesium Carbonate, for example inthe calciner described by Sceats and Horely (PCT Patent Application No.WO2007045048) and included herein in its entirety. These chemicalspecies survive hydration, for example, in the process described bySceats and Vincent (AU2014339743) and included herein in its entirety,to make a stable magnesium hydroxide slurry, with up to 60% of theactive ingredient as Mg(OH)₂. It has been observed that the particlesadhere to the plant leaf, and the particles gradually degrade as themagnesium is ingested through the leaves as a fertiliser, to assist theproduction of chlorophyll. It is believed that, in this prior art, thebio-activity is achieved through the gradual release of ROS, whichprevents the leaf ecosystem from becoming anaerobic, and therebypreventing disease. A common feature of many diseases is that thepathogens initially grow in anaerobic conditions. In that sense, thenano-active materials are disease preventative contact biocides, and thediseases do not develop immunity. The concentration of ROS is generallynot sufficiently high that it has an adverse impact on aerobicbio-organisms. Specifically, the ROS and the alkali, Mg(OH)₂, in theparticles both promote an oxygenated ecosystem, and in such systemspathogenic microbes do not thrive. No substantial persistent bioactivityhas been observed in Mg(OH)₂ produced from MgO produced fromconventional calciners, and this loss is attributed to the sintering ofthe nano-crystalline surfaces, which is correlated with therecombination of the ROS species with the trapped electrons.

In aquaculture, the cultivated species are animals that are generallyvery sensitive to stress, and are intolerant to toxic chemicals thatmight be tolerated by plants. Therefore, the broad spectrum toxicdisease preventatives that are used in agriculture for plants generallycannot be used in aquaculture. Most generally, products that are toxicto humans are also toxic to animals such fish and shellfish. Moreover,the use of drugs developed as disease preventatives for humans, such asantibiotics, show the same evolution as observed in humans, namely theloss of bio-activity over time as the diseases develop strains that areresistant to the drugs. There is a need in aquaculture for diseasepreventative products that are non-toxic to the cultivated species andto humans, and which are broad based in their activity so that thepathogens do not become resistant to the use of the product.

In aquaculture, the cultivated species are fish, mollusks andcrustaceans. The primary method of disease prevention in the cultivatedspecies has been to use successful treatments from land based animalhusbandry. In aquaculture, the most common treatments involve addingbioactive materials to food that is fed to the cultivated species andingested. These treatments often use systemic drugs. However, thequantity of bioactive materials required to achieve disease preventionare very large, and the costs are very high. The poor performance is aresult of the aqueous environment. Soluble compounds may dissolve in thewater before the cultivated species eat the food, and there are largelosses of the bioactive materials. Furthermore, such compounds are takenup by all the species in the water, from plants, plankton, other aquaticanimals, as well as the cultivated species. If compounds are stabilisedin particles, any uneaten particles fall to the bottom of the pond, thenthe bioactive materials are taken up by the benthic ecosystem on the penor pond floor. These practices are generally deemed to be unstainable,and the resistance to diseases in all the biota has the propensity forsignificant undesirable long term effects in the whole ecosystems. Thereis a need for a non-toxic disease preventive that is non-toxic to thecultivated species, but is also beneficial to the environment of thepond, and specifically to the long term healthy ecosystem of the water.Most generally, there is a need for a product for aquaculture that is adisease preventive that has no toxicity impact on the cultivated speciesor the other animal species that inhabit a healthy aquaculture system,including both the aqueous, the benthic and infrastructure ecosystems.The nature of the ecosystems in aquaculture vary significantlythroughout the world because they are dictated by the cultivated speciesnatural habitat and farming practices. The ability to prevent diseasedepends on maintaining healthy aquatic, benthic and infrastructureecosystems.

For example, a particular problem arises in aquaculture ponds that areconstructed from or located near, acid-sulphate soils. Such soils areoften found in areas surrounding mangrove swamps. In mangroves, theconditions are anaerobic and reducing, and iron is deposited as pyrites(ferrous sulphide), which accumulate and persist over geologicaltimescales. When aquaculture ponds are produced from such soils, or thesoils are disturbed, for example, from water run-off and flooding, thepyrites is released into the water and in such oxidising conditions, thepyrites is sequentially oxidised, firstly releasing ferrous and sulphideions, followed by further oxidation to ferric ions and sulphuric acid,such that the pH falls, releasing aluminium ions into solution. The ironand aluminium ions are toxic to species such as prawns, resulting insignificant kills of cultivated species. Eventually, the ions areremoved through the formation of insoluble iron oxide particles, whichare fall into the sludge. On a long timescale, the reducing conditionsin the mud form pyrites, and the cycle will continue when the mud isdisturbed and exposed to oxygen. There is a need for a material that canbe added to the water in a new aquaculture pond, or a pond that has beendisturbed by flooding, that not only prevents pathological disease frommicrobes for such cultivated species, but which also rapidly removes thetoxic iron and aluminium ions from solution.

The heavy metals, such as cadmium copper, lead, chromium, arsenic,barium cobalt, manganese and vanadium are toxic to most cultivatedspecies in aquaculture. The bigger problem is that these metals may beconcentrated by accumulation, such as in the gills of fish, through theuse of recirculated water, or by natural events (floods and the like).The major issue is generally not the toxic effects on the cultivatedspecies because the concentrations are normally low, but the healthimpact on humans arising from the accumulated levels of heavy metals inthe human body over a long time from eating such cultivated species.There is a need for a material that can remove heavy metal ions fromaquaculture ponds.

A more general issue arises from the water contamination from excretionswhich cannot disperse because of the dense population, the high foodconsumption, and low water flow. Of particular concern is the highconcentrations of phosphorous, as phosphate ion, and nitrogen, as ureaand ammonia. These may cause eutrophication and hypoxia, in the pond orin downstream water. Increasingly, aquaculture farmers are underpressure to reduce the leakage of these materials from aquaculture pensand ponds. There is a need to remove phosphorous, as phosphate, andnitrogen, generally as ammonia, from aquaculture pens and ponds on thebasis that excess amounts of these cause stress on the cultivatedspecies, but also adversely impact on the environment in and around theaquaculture ponds. There is need to remove excess phosphorous andnitrogen from the water in aquaculture pens.

The prior art of Sceats, and Sceats and Hodgson, cited above, disclosesthe production and use of nano-active materials from carbonate compoundsto produce a biocide for application in agriculture and aquaculture, andother applications such as protection of food to infestation of microbesthat induce diseases in humans. The carbonate precursor identified inthat patent is the mineral magnesite, MgCO₃. Magnesite is a relativelyrare mineral, and is usually characterised by a significant amounts ofimpurities including sand, dolomite, talc and clay. Beneficiating themineral to achieve high purity mineral feedstock is costly. There is aneed to extend the range of precursors that can be used to producenano-active Mg(OH)₂.

Any discussion of the prior art throughout the specification should inno way be considered as an admission that such prior art is widely knownor forms part of common general knowledge in the field.

SUMMARY Problems to be Solved

It is an object of the present invention to provide a process tooptimise the product for the specific use in aquaculture, where theproduct is to be bio-active in both the aquatic and benthic ecosystems,and to be a non-toxic food additive for ingestion by the culturedspecies.

It is an alternative object of the present invention to provide aprocess to manufacture a product or a product for the restoration theaqueous ecosystem in aquaculture which may be adversely impacted byheavy metals, by eutrophication from phosphorous and nitrogen, andexcess turbidity from solid particulates such as clays and iron oxide.

It is another alternative object of the present invention to provide aprocess to manufacture a product or a product for the restoration of thebenthic ecosystem in aquaculture which may be adversely impacted byseptic conditions.

It is yet another alternative object of the present invention to provideThe prior art of Sceats and Hodgson claimed the application inaquaculture, and subsequent tests demonstrated that the performance maybe enhanced by more specific specifications, now claimed in thisinvention.

It is an alternative object of the present invention to reduce theadverse impact of biofilms on the infrastructure of the aquaculture pondor pen, and more generally for all marine infrastructure, such as ships,boats, buoys, and wharves.

Means for Solving the Problem

A first aspect of the present invention provides a process for producinga biocide powder, comprising the steps of:

-   -   Selecting one or more carbonate compounds with a predetermined        calcium/magnesium ratio;    -   Grinding the carbonate compounds to produce a carbonate powder        with a first predetermined particle size distribution;    -   Selecting a magnesium hydroxide compound;    -   Grinding the hydroxide compound to produce a hydroxide powder        with a second particle size distribution;    -   Calcining the carbonate powder in an externally heated        counterfiow flash calciner at a first temperature to produce a        calcined mixture having a surface area sufficiently high enough        to exhibit bioactivity;    -   Calcining the hydroxide powder in an externally heated        counterflow flash calciner at a second temperature to produce a        calcined oxide with a surface area sufficiently high enough to        exhibit bioactivity; and    -   Blending the calcined mixture and the calcined oxide in a        predetermined proportions.

Preferably, the process further comprises the step of adding groundlimestone, or lime or hydrated lime to the form the biocide powder.

Preferably, the carbonate compounds comprising Magnesite and Dolomite.

Preferably, the degree of calcination of the magnesium carbonate in themagnesite and dolomite is in the vicinity of 95% or more, and the degreeof calcination of the calcium carbonate is in the vicinity of 5% orless.

Preferably, wherein the calcined mixture and calcined oxide comprisesmagnesium oxide (MgO).

Preferably, the surface area of the magnesium oxide is ranged from 200m²/gm to 300 m²/gm.

Preferably, the magnesium hydroxide compound comprises mineral bruciteor magnesium hydroxide powder produced from seawater or brine in whichthe degree of calcination of the magnesium hydroxide is around 95% ormore.

Preferably, the surface area of the oxide from the hydroxide powder isabove 200 m²/gm of MgO, and preferably above 250 m²/gm of MgO and mostpreferably above 300 m²/gm of MgO.

Preferably, the particle size distribution of the ground carbonatecompounds is in the range of about 1 to 100 microns, with the particlefraction in the range of 1 to 10 microns.

Preferably, the particle size distribution of the ground magnesiumhydroxide compound is in the range of about 1 to 100 microns with thedistribution in the range of 1 to 10 microns.

Preferably, the particle size of the ground limestone or lime is in therange of about 1 to 100 microns.

Preferably, the blend of the powder produced from carbonate; the powderproduced from hydroxide depends on the availability of the carbonate andhydroxide input materials and the specification to achieve apredetermined Ca/Mg ratio.

Preferably, the proportion of limestone, lime or hydrated lime dependson the specification to achieve a desirable Ca/Mg ratio for theapplication and to achieve a desirable viscosity and stability of theslurry in conjunction with the amount of carboxylic acid added in theslurry production process.

Preferably, the first temperature is different to the secondtemperature.

Preferably, the first temperature is about 750° C.

Preferably, the second temperature is about 450° C.

Preferably, the process further comprises the step of:

-   -   Hydrating the biocide powder with water at or near the boiling        point of water until the hydration is completed;    -   Applying a shear mixing, and    -   Adding a carboxylic acid or salt as the thinning agent    -   in order to form a stable, readily thinned, slurry of the        hydrated oxide with about 60% solids in the final product.

Preferably, the process further comprises the step of quenching theslurry to below 60° C.

Preferably, the process further comprises the step of cooling the slurryto ambient.

Preferably, the process further comprises the step of adding additivesto the slurry

Preferably, the additive is an aqueous solution of hydrogen peroxide.

Preferably, the additive is ozone, which is sparged into the slurry.

Preferably, the biocide powder is adapted to use in agriculture, food,water treatment, chemical detoxifier, and industrial applications suchas rubber production, the Ca/Mg ratio being around 5% to less than 2%.

Preferably, the biocide powder is adapted to use in aquaculture, theCa/Mg ratio being around more than 5% to 15%.

Preferably, the biocide powder is adapted for an application as abiocide spray, a foam or a fog wherein the slurry or powder is mixedwith oil to form an emulsion if required, and processed into a foam orfog.

Preferably, the biocide powder or slurry product for application as abiocide paint, including a marine paint to prevent biofilm growthwherein the slurry of powder is mixed as a filler into a paintformulation that may be either water or oil based.

Preferably, the carboxylic acid is acetic acid, and the carboxylic saltis magnesium or calcium acetate.

In another aspect of the present invention, there is provided a reactionapparatus for producing biocide powder or a chemical detoxifier powderor a catalyst support from a carbonate mineral, comprising:

-   -   a grinder for carbonate compounds    -   a grinder for hydroxide compounds    -   an externally heated counter flow flash calciner that produces        high surface area oxides from the ground carbonate;    -   an externally heated counter flow flash calciner that produces        high surface area oxides from the ground carbonate; and    -   a blender in which the calcined solid powders are mixed        together, and or with other ground solids for the production of        a biocide powder.

Preferably, the reaction apparatus further comprises a hydrationreaction vessel for the production of the slurry product having an inletfor the blended powder and a water inlet and a shearing apparatus forshearing the reaction mixture; and a steam outlet for release of steamfrom the reaction vessel, such that in use the reaction is controlled byallowing heat of hydration to raise the temperature of the reactionmixture, allowing water to boil off from the reaction mixture ashydration proceeds, and removing steam via the steam outlet to removeexcess heat and control reaction temperature at boiling point and ameans of quenching the slurry to below 60° C., preferably by transfer ofthe slurry to a cooled container and a means of cooling the slurry toambient temperature; and a means of adding solid or liquid additives tothe slurry.

Preferably, the reaction apparatus for post-processing the bioactivepower or slurry from the apparatus by one or more of the followingsteps:

-   -   sparging the powder or slurry with a gas adjuvent such as ozone        to enhance bioactivity; or    -   adding and mixing liquid adjuvent compounds to the powder or        slurry to enhance bioactivity; or    -   adding and mixing materials to the powder or slurry to make a        biocidal coating product or    -   adding and mixing materials to the powder or slurry to make a        biocidal emulsion or foam

In another aspect of the present invention, there is provided a chemicalcomposition as a powder adapted for use as a biocide, wherein thecomposition comprises: a powder of micron scale calcined particles whichare formed from a mixture of carbonate compounds and hydroxidecompounds, and which have additives to boost the biocide impact such asozone, hydrogen peroxide wherein the particles have a porosity ofgreater than 0.5 and wherein the pore surface is largely composed ofnano-crystalline structures.

Preferably, the chemical composition is presented as a slurry adaptedfor use as a biocide, wherein the composition comprises a slurryproduced by hydrating the powder with additives that stabilise theslurry.

Preferably, the chemical composition is presented as a coating materialslurry adapted for use as a biocide, wherein the composition comprises acoating material produced by mixing the powder or the slurry withadditives that set the material when applied to a surface.

Prefer the chemical composition is presented as a foam, spray oremulsion material slurry adapted for use as a biocide, wherein thecomposition comprises a foam, spray or emulsion material produced bymixing the powder or the slurry with additives that form a foam, sprayor emulsion when processed.

In the context of the present invention, the words ‘comprise_,‘comprising_ and the like are to be construed in their inclusive, asopposed to their exclusive, sense, that is in the sense of ‘including,but not limited to_.

The invention is to be interpreted with reference to the at least one ofthe technical problems described or affiliated with the background art.The present aims to solve or ameliorate at least one of the technicalproblems and this may result in one or more advantageous effects asdefined by this specification and described in detail with reference tothe preferred embodiments of the present invention.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 depicts a schematic drawing of a process for production of apowder or a slurry from powders of mineral magnesite, dolomite orbrucite in which the powder particle size, porosity and surface area areoptimised by calcination to form a biocide.

DESCRIPTION OF THE INVENTION

Preferred embodiments of the invention will now be described withreference to the accompanying drawings and non-limiting examples.

FIG. 1 depicts a schematic drawing of a process for production of apowder or a slurry from powders of mineral magnesite, dolomite orbrucite in which the powder particle size, porosity and surface area areoptimised by calcination to form a biocide.

One example form of manufacture of the product which can be described byconsideration of the process flow of FIG. 1 for the mineral precursorsof magnesite and dolomite as carbonate compounds and brucite as ahydroxide compound. Other minerals particulate impurities in a minedmineral may include sand, talcs, and clays. The desired material productis either a bioactive powder or a bioactive slurry. The desired solidproduct may be made solely from the carbonate materials, or thehydroxide materials, or a combination of either, and a by-product fromthe carbonate compound processing may be a pure carbon dioxide gas.

The hydroxide compound may be a mineral brucite or a synthetic brucitefor example, produced from sea water or brines in the known art byprecipitating the hydroxide from sea water or brines by the addition oflimestone. The synthetic material is called herein brucite, although itmay have a different crystalline structure from the mineral.

In this embodiment, the 10 comprises the following steps:

-   -   Grinding the feedstocks (steps 12 a, 12 b);    -   Calcining the ground materials (steps 14 a, 14 b);    -   Blending the calcined materials (steps 16);

In another embodiment the process 10 may comprise a further step ofadding ground limestone, or lime or hydrated lime to the form thebiocide powder.

In yet another embodiment, the process 10 may comprise a further step ofhydrating the blended powder to form a slurry product (step 18).

In yet another embodiment, the process 10 may further comprise a step ofenhancing the bioactivity of the slurry with adjuvents as an option(step 20).

In one embodiment of the present invention, the first step of process 10is one in which the desired particle size distribution is achieved bycrushing and grinding the compounds (steps 12 a, 12 b). The magnesiteand brucite are the primary sources of nano-active Mg(OH)₂ in the finalproduct, whereas the dolomite is the primary source of calcium. Theseminerals may be found within a mine site and are selectively mined, orin the case of brucite, synthesised. In this embodiment the hydroxidecompound are ground separately from the carbonate compound. It is knownin the art that the brucite grinds very differently to the otherminerals by virtue of its different crystal structure, which is suchthat the mineral rapidly flakes to during grinding give small particlesin the range of 0.4-15 microns. In this embodiment, the process forproduction of brucite is taken to be unchanged from that used to make,for example, brucite for the manufacture of refractories, in which theprocess is optimised to facilitate ease of filtering, drying andcompacting for subsequent calcination in a kiln. That is, the particlesize distribution exceeds the preferred distribution of say 0.4-100microns. In this embodiment, the dried particles are ground. This maypreferably be done by first sieving the particles to remove the fractionabove 100 microns, and then grinding the oversized fraction to produceparticle with sizes in the range of 0.4-15 microns. A number of sievingand grinding stages can be performed to give the desired particle sizedistribution for the application.

In this embodiment, the desired particle size distribution of the groundcarbonate compound may be achieved in a number of grinding stages,followed by mixing. For example, a single grinding process may notprovide a sufficient number density of small particles, such that afraction of the coarsely ground material may be finely ground, andremixed with the residual coarsely ground fraction. The art of obtaininga desired particle size distribution by such comminution processes is aknown art per se. The desired particle size distribution is typically inthe range of 0.4-100 microns.

In this embodiment, the fraction of dolomite in the ground material isset to give the desired calcium/magnesium ratio for the desiredapplication. For example, in aquaculture, For aquaculture, a typicaldesirable Mg/Ca ratio on a molar basis is in the range of about 6:1-4:1.While it is possible to use ground limestone as the source of thecalcium, the availability of the calcium carbonate from limestone islower than that which is available from the calcined dolomite, describedbelow, by virtue of the higher porosity and surface area of the calcineddolomite compared to ground limestone.

The second step of the sample embodiment is calcination. The groundcarbonate compound is processed by calcination, as described by Sceatsand Hodgson to create the nano-scale crystallites that are believed tobe the source of the bioactivity. This step of the process is that ofcalcination of the carbonate in which the MgCO₃ in the magnesite anddolomite is calcined. It is important that the processed particlesexhibit minimal sintering during the calcination process, and achieve adegree of calcination of the MgCO₃ sites, in the magnesite and dolomite,that is preferably in excess of 95%. The most fundamental measure of thedeleterious impact of sintering is the specific surface area Theexperimental results show that the calcination of the dolomite MgO sitedoes not generate nano-scale crystallites of MgO with super-oxideformation to create a biocide. Without being limited by theory, it isreasonable to assume that the uncalcined CaCO₃ moieties in the dolomiteprevents the formation of MgO nano-crystallites because there isinsufficient time during flash calcination for diffusion and aggregationof nano-structured MgO to occur, as reasoned by Sceats and Haley inAU2006904553. Extending the time leads to sintering and phase separationwith no nano-scale crystallites. The surface area that provides thebio-activity of the calcined product is that of the MgO from magnesitealone. This can be deduced from surface area and calcinationmeasurement, and should be 200 m²/gm of MgO from magnesite, andpreferably greater than 250 m²/gm of MgO and more preferably greaterthan 300 m²/gm of MgO. The type of calciner is critical to achieving theproperties described above. The basic requirement is that the process isvery fast to eliminate the effect of sintering, and this should bepreferably several seconds. This means that the process is flashcalcination. The second requirement is that the particles experience thelowest possible temperature during this time. Conventional flashcalciners drop the particles into a very hot combustion gas, and fromthat time, the temperature of the gas decreases as the react on extractenergy from the gas stream. Further, not all particles experience thesame conditions. The net result is that the outer surfaces of theparticles are extensively sintered, and it is difficult to achievesurface areas in excess of 50 m²/gm of MgO. The small particles are mostextensively sintered. The preferred calciner is that described by Sceatsand Horely, for example in WO2007/112496 (incorporated herein byreference). In this case, the temperature of the particles flowingthrough the calciner steadily increases for all particles, and themaximum temperature they experience is the exhaust temperature. Duringthe calcination, there is generally some decrepitation of the inputparticles, and often a shoulder appears on the particle sizedistribution in the region of 0.1-1 microns. Control of the externalburners along the calciner provides the desired heat transfer to theparticles, and the degree of calcination and surface area can becontrolled. This system is known per se, and is capable of operating atproduction levels of about 5 tonnes per hour for particles that are 95%calcined for the Mg site, with a surface area of greater than 200 m²/gmof MgO from magnesite. The important factor which determines thebiocidal impact is the high surface area of the MgO from the magnesitein the calcined powder. For the calcination of magnesite and dolomitethe exhaust temperature from the calciner is preferably about 750° C.,at which temperature about 95% calcination of the MgCO₃ is achieved,less than about 3% calcination of the CaCO₃ is achieved.

The calcination process for the ground hydroxide compound is similar tothat described above for the ground carbonate compounds, except that thetemperature of the exhaust of the calciner is preferably lower thanabout 450° C., at which temperature 95% calcination of the Mg(OH)₂ tonano-active MgO is achieved with a surface area greater than 120 m²/gmof MgO. This process has not previously be described. Generally,multiple hearth furnaces can produce MgO from magnesium hydroxide with asurface area of typically 50-100 m²/gm, and such MgO does not displaythe required nano-active properties required for biocidal activity. Athigher exhaust temperatures of above about 450° C., for a givencalciner, the sintering of the particles dramatically reduces thesurface area.

It highly desirable that the calciner design, of the type, for example,described by Sceats and Horely, is its capability for processing eitherthe hydroxide compound at about 450° C. or the carbonate compound atabout 760° C. That is, in the embodiment of FIG. 1, the two calcinersshown can mean the same equipment operating under different settings atdifferent times.

The third stage of the embodiment of FIG. 1 shows that the powderstreams from the two calcination processes being mixed to form thebiocide powder product. This product has the desired particle sizedistribution and the Ca/Mg ratio to suit the application. This powder isa biocide, and can be used in application where a powder form is used,either directly or indirectly as a feed for the manufacture of productssuch as coatings.

Where a slurry product is desirable, the fourth stage of the process isto hydrate the slurry. This process is well described by Sceats andVincent for example in AU 2013904096 (incorporated herein by reference),as a process that can produce tonnes of slurry per hour to match theproduction rate of the calciner described above. The high surface areaof the particles is such that the hydration reaction, when mixedvigorously, liberates a large amount of heat and boils the water. Thisestablishes a set point and the thermally activated hydration occurs atthe boiling point and the excess heat is liberated by boiling. Theapplication of a shear mixer provides the agitation required for auniform controlled process. During the course of the reaction, aceticacid is added to the slurry to provide thinning necessary for the shearmixer to operate. The reaction is complete when the temperature startsto drop from the heat losses. It is preferred to quench the slurryquickly below 60° C., and then let the slurry cool to ambient for thenext processing step. The net result is a slurry that has hydrated, andwhich is stable over many months with regard to sedimentation, and whichis readily shear thinned to allow pouring and processing. This slurryhas the same intrinsic biocide activity as has nano-particles whendiluted in water for application as a foliar spray. Importantly, thereis no significant loss of biocide activity during over the slurrylifetime of several months.

The fifth stage is the option, if required, to add adjuvants to eitherthe powder or the intrinsic slurry product described in order toincrease the biocide properties above that of the intrinsic biocideresponse considered below. There are many such adjuvants. Examples arehydrogen peroxide, or ozone, which can be added to saturate thecrystalline binding sites on the Mg(OH)₂ surfaces with the radicalspecies being the superoxide ion, the hydroperoxide anion, and oxygenradical, and the hydroxyl radical. Magnesium peroxide MgO₂ is a stablecompound. In addition, the acetate ions may be further converted to theperoxyacetate ion, which is stable at the pH of the slurry, at about10.4. Impurity ions, such as Fe²⁺ and Fe³⁺ are removed from the slurryas particles for ferric oxide. The use of hydrogen peroxide or ozonesupplements the intrinsic radicals developed during calcination andhydration. Ozone is added by sparging the slurry with ozonated air.Other adjuvents include a large number of established biocides,including all those listed in U.S. Pat. No. 6,827,766 B2 ornano-particles such as AgO and ZnO. Depending on the specific adjuvantand the amount added, the stability of the slurry may have to bere-established by the addition of dispersion agents. The use ofadjuvants is not generally preferred because it may make the producttoxic to humans, and increase the cost of production compared to theintrinsic biocide developed in the previous stages.

If required, impurities in the mineral such as sand, talc and magneticparticles are extracted during this process at any stage. The process tobe used depends on the mineral source, whether macrocrystal line orcryptocrystalline, the impurities, the grinder and the grinder settings.Generally, for aquaculture applications, no such separation step isrequired.

Most importantly, it is noted that there is an expectation that thereare no nanocrystalline particles present (i.e. with a diameter less than0.1 microns) in the powder or slurry, and generally such particles areundesirable because, as fines, they are difficult to filter from thegrinder air, and also to process in the steps described below, and tomeet customer and community concerns about the toxicity of nanoparticlesin general. The grinders are preferably grinding mills that entrains theground particles in air, and which removes particles above about 0.5-1micron before they can be further ground. This is a known art per se.

The intrinsic biocide for aquaculture produced using steps 1-5 describedabove produces either a powder or a 60% solids slurry of particles witha range of particle sizes from 0.1 microns to 100 microns as measured bya particle size analyser, and a Mg/Ca ratio in the range of 4-6.

The biocide activity of the intrinsic powder and slurry in aquaculturehas been established in preliminary aquaculture trials on crayfish,prawns, salmon, tilapia, sea bass, silver perch, trout and milkfish.

The milkfish trials were conducted on fingerlings over 13 weeks in a 4ha pond of 0.85 ML stocked with 250,00 fingerlings that are fed 3 timesper day. The water is drained every 2 weeks. Weekly doses of 60 kg ofthe slurry were used. The pH was about 8.0-8.5. The odour of H₂S was notpresent, compared to the control, and samples of the pond bottom weremore solid, had less odour, and were lighter in colour. The fingerlingmortality was 55% compared to 65% in the control, and the weight of thefingerlings was 34.9 g, compared to 22.4 g in the control. Thus theyield improvement was 84%. The fingerlings were transferred to sea pens(without further treatment), and at the harvest, the average fish weightwas 7.3 kg, compared to 6.6 kg for the control. The quantity of premiumfish, with the highest weight increased by a factor of 4. The economicimpact was estimated to be ten times higher than the cost of dosing.

The biocide activity of the intrinsic powder slurry for agriculture andother applications has also been established, and are the same asdescribed by Sceats, and Sceats and Hodgson.

In one embodiment of the present invention, the nano-activity isdemonstrated when brucite is used as a starting material. Brucite is themineral of Mg(OH)₂ which is formed in a slow process where the grainsize or crystallite size is in the region of microns and larger, andwhen ground, the particles exhibit no bioactivity. Brucite may besynthesised from sea water or brines by treating such with lime ofhydrated lime to precipitate the Brucite. This brucite also exhibits nosubstantial bioactivity. When the brucite is flash calcined to give avery high surface area MgO, the MgO is formed as nano-scale crystalliteswithin the particle, and hydration creates nano-scale Mg(OH)₂ within theparticles. There is no observable change in the particle size, so thatthe process has transformed the structure of the brucite frommacrocrystalline to nanocrystalline, and the defect density isaccordingly very high, and the nano-activity is accordingly high.

The sprayed slurry of the hydrated nano-active Mg(OH)₂ has the effect ofa disease preventative contact biocide, and is not a systemic biocide.The implication is that it has a broad spectrum response, typical ofother biocides such as sulphur and copper compounds, and hydrogenperoxide, but without the toxic effects on all the biota on the leafecosystem. An advantage of the nano-active particles is that thepotentially adverse toxic impact of nano-particles on humans ismitigated because the particles cannot be breathed into the lung, andcannot diffuse through the skin into the human blood and lymph systemsbecause the particles are too large. If ingested into the human gut, theparticles are rapidly dissolved by the acids in the stomach. At highconcentrations, the release of magnesium ions in the human or animal guthas the mild muscle relaxant effect of Milk of Magnesia.

In one embodiment of this invention, the materials described by Sceatsand Hodgson are extended to include marine applications generally, incombination with other materials to form a setting material that, as abiocide, inhibits the formation of biofilms.

A first aspect of this invention may include the extension of theprecursors that can be used for the production of the nano-activeMg(OH)₂ biocide described by Sceats and Hodgson, and the variation ofthe process conditions to achieve the biocidal properties. The prior artof Sceats and Hodgson claims a production process of carbonate mineralswith the first step being grinding the precursor to produce a powderwith a broad particle size distribution. The specification of thenano-active Mg(OH)₂ material was a particle size in the range of 0.5-100microns. The feedstock for this prior art was generally magnesite, whichis not abundant and is usually found with mineral impurities. In thisinvention, the range of preferred mineral precursors is increased fromcarbonatites such as magnesite MgCO₃ and dolomite MgCO₃.CaCO₃ to includebrucite, Mg(OH)₂, where brucite include the mineral as well as syntheticmagnesium hydroxide produced from brine, as a known art per se.Subsequent experiments have shown that magnesium hydroxide crystals madefrom brine itself are not nano-active because their surface area is toolow. However, nano-activity can be induced by flash calcination ofbrucite to a nano-active MgO, followed by rehydration to form anano-active Mg(OH)₂ material in the process described herein. Theinvention requires significantly different processing conditions thatare disclosed herein. The synthetic brucite typically has a broaddistribution of crystal sizes with a significant fraction above 100microns, such that further grinding, wet or dry, is required to give apreferred distribution. The synthetic brucite material has beendeveloped for ease of processing and for applications such as refractorymanufacture in which the crystal size is generally as large as possible.For this invention, smaller crystal sizes are required, and theinvention recognises that the synthetic process for brucite can bemodified to yield a crystal size distribution that meets therequirements for this invention. Therefore, the first step in thismodified process is one in which the size distribution may be achievedby either grinding or synthesising the precursors to give the desiredparticle size distribution. The first step can include grindingdifferent fractions of the raw materials in a number of fractions to anumber of different degrees of grinding and remixing the fractions togive the desired distribution, or including within a grindersegmentation of the materials to achieve the desired particle sizedistribution. The first step can include synthesising the precursor in anumber of stages to give the desired distribution. For example, withsynthetic brucite, boron can be used to control the crystallitedistribution as described by Chisholm in U.S. Pat. No. 3,232,768.

A second aspect of the present invention may include the production of anano-active product that can simultaneously provide bioactivity in theaqueous and the benthic ecosystems of an aquaculture pen or pond. Inorder to achieve a simultaneous impact, the product must be provided toboth these ecosystems in doses that enable them to respectively impacton pathogenic species in each ecosystem. The general means of dosingused in aquaculture ponds is to deliver the product from a spray in aliquid form, or a metered spray of the liquid form or a powder form onthe surface of the pond or pen. It has been found that the mostadvantageous distribution between ecosystems can be achieved bycontrolling the particle size distribution. It has been observed thatvery small particles, say below 10 microns in diameter have a very longresidence time in the aqueous ecosystem. This is because their settlinghydrodynamics is dominated by Brownian motion from the water, such thatthe settling velocity of such fine particles from the aqueous ecosystemis very low. This gives a prolonged residence time, so that theencounter of the particles with a pathogen is sufficiently probable thatthe bioactivity of the particles can exert themselves in this ecosystem.The fine nano-active particles can adhere onto the pathogen for directbio-impact or the cultured species or algae for indirect bio-impact. Ithas been observed that larger particles, say above 50 microns, have ashorter residence time in the aqueous environment because theirhydrodynamics is dominated by gravitation, offset by turbulence of thewater, such that they quickly fall into the benthic environment wherethey can exert their bio-impact Intermediate sized particles haveintermediate residence time. The most desired residence time depends onthe location of the pathogen and the life-cycle of the pathogen. Forexample, some pathogens initially grow in benthic layer, before makingan impact on the cultivated species. Therefore, the most effective meansof controlling the residence time is to control the particle sizedistribution of the particles so that a sufficient fraction of theparticles fall directly into the benthic ecosystem. Thus there is apreferred fraction of fines in the range of 0.4-10 microns that have along residence time in the aqueous ecosystem, and course largerparticles in the range of 50-100 microns that have a short residencetime in that ecosystem, so that they act to improve the benthicecosystem.

The specification of 0.5-100 microns was developed by Sceats and Hodgsonto be such that the calcination process and the formation of a stableslurry could be readily achieved. For aquaculture, experiments haveshown that the particle size distribution is preferably furtherspecified to meet the residence time distribution of the particles inthe aqueous ecosystem and the benthic ecosystem so as to have maximumbio-impact for the health of the cultivated species, as well as meetingthe requirements for calcination and slurry stability. The preferredrange of the particle size for aquaculture applications is within the0.5-100 micron range claimed by Sceats and Hodgson, and is hereinfurther specified for use in aquaculture. Thus key feature of thisinnovation is that the particle size distribution has become a parameterto optimise the biocidal impact of the nano-structured particles, ratherthan just a specification for the ease of calcination and stable slurryproduction. For example, for controlling the parasite vibrio in prawns,for an aquaculture pond that was 2 metres deep, the desirable particlesize was such that at least 30% of the particles were less than 5microns.

A third aspect of the invention is associated with the ingestion of theparticles by the cultivated species. The prior art described by Sceatsand Hodgson is focused on the use of nano-structured particles inagricultural crops, where the ingestion of the particles through theleaf stomata provides an additional benefit of enhancing the growth ofthe plant by the adsorption of magnesium for the production ofchlorophyll. However, by analogy, the ingestion of the particles by thecultivated species in aquaculture provides a means of providing mineralsfor growth. The cultivated species have specific requirements forcalcium for the growth of bones or shells, and the aqueous ecosystem maynot be able to supply the required amounts. Further, calcium is alsoimportant in fish hatchery water supplies, because eggs tend to hydrateat low calcium concentrations and may not develop or hatch if thecalcium concentration is too low. The cultivated species may ingest thecalcium from the ions in the water (ie through the calcium hardness,which varies from lakes, rivers, estuaries and the sea) and from food,either directly or from algae that grow in the pond, or from additivessuch as calcium sulphate. The nano-active material is generally Mg(OH)₂produced from hydration of MgO from calcining magnesite ores. Mostmagnesite ore, dominantly MgCO₃ contains some dolomite MgCO₃.CaCO₃. Whenthe dolomite ore is processed, the product is a semi dolime MgO.CaCO₃,and the formation of dolime MgO.CaO is suppressed at low calcinationtemperatures by the high partial pressure of CO₂. This process isdescribed by Sceats and Horely (AU 2006904553), incorporated herein forreference. The dolomite crystallites are often found within the groundmineral feedstock particles along with magnesite and silica. Experimentshave shown that the high porosity and surface area of the semidolimeproduced in the flash calciner is such that the hydrated material,Mg(OH)₂.CaCO₃ exhibit a very fast acid decomposition which releases thecalcium ions. In the gut of the fish, the acids in the stomach quicklyrelease the calcium which can be ingested and can assist in the growthof the fish. It is preferable that the conditions of the calcination issuch that the CaCO₃ is not calcined to lime. The absence of lime CaO, asdolime MgO.CaO, is such that the pH within the particle is maintained atabout 10.4, and experiments have shown that the intake of the hydratedsemi dolime in the hydrated product has no adverse effects from stressthat otherwise may have occurred had quicklime been formed. Thedesirable Mg/Ca balance in the product can be optimised to meet therequirements of the cultivated species, taking into account the calciumand magnesium in the water and in the food. Generally, the use of amixture of Magnesite and dolomite as feed into the calciner can bevaried so as to deliver the required Ca/Mg dose for growth of thecultivated species. More generally, mineral deposits of magnesite arefound in layers, usually accompanied with dolomite layers, and themagnesite rich layers have some Dolomite as granular impurities andsubstitutional impurities. This benefit of specifying a Ca/Mg ratio isan important feature for aquaculture, but relatively unimportant forplants. Thus the specification for the production of the bioactivematerial by Sceats, and Sceats and Hodgson, failed to teach the benefitsof controlling the input mineral to provide the desired bioactivity, andthe desired Mg/Ca ratio in aquaculture applications to promote thehealth of the cultivated species, specifically with respect to thegrowth of bones and the hatching of eggs. This capability relies on thelack of toxicity of the nano-active species for ingested particle'sbecause the acids in the stomach dissolve the particles and the releasedROS is at sufficiently low doses that they are rapidly reduced in thedigestive tract. The animal cells are capable of handling intense burstsof ROS because the release of ROS is a primary mechanism developed tocombat infection. Thus nano-active particles have no toxicity to thecultivated species when ingested, and it is desirable that the calciumrequired for bones and shells is provided as CaCO₃, in particles with ahigh surface area so that ingestion is rapid. Thus calcined dolomite ispreferable to the addition of ground limestone because the calcium ismore accessible from semidolime because of the higher surface areaarising from calcination of the magnesium site.

A fourth aspect of the invention relates to the ability of the particlesthat are suspended for a short time to remove heavy metals, and excessphosphate and nitrogen, from the aquatic ecosystem. The specificationprovided by Sceats and Hodgson uses the surface area and porosity of themagnesium oxide as indicators of the nano-crystallinity of the powder,and therefore as indicators of the propensity of the particles togenerate ROS at the nano-grain boundaries, and to retain these speciesas oxidants after hydration. However, experiments in aquaculture haverevealed that the surface area of the magnesium hydroxide itself enablesthe controlled removal of heavy metals and phosphorous and nitrogen fromthe aquatic ecosystem during their passage to the floor of the pen. Theaccumulation of heavy metals, such as cadmium, copper, lead, chromium,arsenic, barium, cobalt, manganese and vanadium in the cultivatedspecies may make the product unsuitable for human consumption. Very highconcentrations of iron, from pyrites oxidation, are toxic to the fish.Magnesium hydroxide is well established as a product for removing ironand heavy metals from soils and water, where the metals precipitate toform insoluble hydroxides. Experiments have shown that the extractionefficiency is enhanced by the high porosity and surface area of theMg(OH)₂ particles. Without being bound by theory, the reason for this istwo-fold. Firstly, the reaction kinetics for the precipitation ofinsoluble hydroxides scales with the surface area of the Mg(OH)₂, andsecondly, within the pores of the particle, the concentration ofhydroxide ions is that of water saturated by the dissolution of Mg(OH)₂at the pH of 10.4, rather than the pH of the water itself, which ispreferably in the range of 7.0-7.6 for aquaculture. Thus the particles,falling through the water, efficiently extract the heavy metals from theaqueous ecosystem without the need for the particles to raise the pH tothe levels required for heavy metal precipitation. These largerparticles, having accumulated the metals, fall into the sludge of thebenthic ecosystem. It is now current practice to extract the sludge fromthe pen after a number of days, and in this case, the heavy metals ionsare removed from the pen. In the sludge, the larger particles sequesterthe heavy metals in the same way as Mg(OH)₂ is used to sequester heavymeals in soils, with a very low rate of leaching. It is preferable thatthere is a sufficient fraction of particles move through the aqueousecosystem and fall into the benthic ecosystem to remove heavy metalsfrom the aqueous system, and that there is a sufficient amount of suchparticles in the sludge, when removed, such that the heavy metals areextracted from the benthic ecosystem. Experiments have shown that theuse of low surface area, low porosity Mg(OH)₂ is not as efficient forheavy metal extraction. The invention is that the high porosity andsurface area increases the yield of heavy metal ions that would beexpected on the basis of the pH of the aqueous ecosystem.

In a similar manner, excess phosphorus, as the phosphate ion, andnitrogen as the ammonium ion, precipitate magnesium phosphate andmagnesium ammonium phosphate in the particle pores at the pH of 10.4 andat a concentration of magnesium that is or order unity (directly from asurface site), and these materials are collected in the sludge. It ispreferable that there is a sufficient fraction of particles move throughthe aqueous ecosystem and fall into the benthic ecosystem to removeexcess phosphorous and nitrogen from the aqueous system, and that thereis a sufficient amount of such particles in the sludge, when removed,such that the excess phosphorous nitrogen are extracted from the benthicecosystem. It is noted that excess nitrogen is extracted when there isexcess phosphate. In the case that the heavy metal ions are sufficientlylow, the sludge is a useful plant fertilizer. Experiments have shownthat the use of low surface area, low porosity Mg(OH)₂ is not asefficient for excess phosphorous and nitrogen extraction. The inventionis that the high porosity and surface are increases the yield of excessphosphorus and nitrogen that would be expected on the basis of the pHand magnesium concentration in the aqueous ecosystem.

Therefore, in this innovation, the high surface area and porosity of theMg(OH)₂ particles have been shown to control the extraction of heavymetal ions, phosphorous and nitrogen from the aqueous ecosystem, suchthat the cultivated species can grow healthily in a clean ecosystem, andthe cultivated species can be consumed without adverse health impacts tohumans.

A fifth aspect of the invention is associated with the capability of theMg(OH)₂ particles to induce the flocculation of the particles in theaqueous phase. These particles may be suspended clays from soilsfollowing run off or disturbance, or organic matter such as faeces oruneaten food. In aquaculture practice, the optimum turbidity of the pondis dependent on the needs of the cultivated species, and generally itshould not be too high to induce health problems, or too low tofacilitate the capture by predators, such as birds. Magnesium hydroxideis an established flocculant because its high charge density causes thecollapse of ionic boundary layers which others keeps the particles insuspension. Without being bound by theory, the Mg(OH)₂ particle have apoint of zero charge at a pH of 10.4, and are thus negatively charged inan aqueous ecosystem with a pH in the ideal range of 7.5-7.0, whereasthe particles that cause the turbidity and health problems have a pointof zero charge below a pH of 7.0 and are charged positively. This is thebasis of why Mg(OH)₂ is an excellent flocculant. However, the highsurface area is such that the local response of these particles is fast,and the floc forms quickly through the charge neutralisation.Experiments have shown that the efficiency and rate of flocculation of ahigh porosity high surface area Mg(OH)₂ particle is larger than acomparable Mg(OH)₂ particles that have a lower surface area and lowerporosity. Generally, this process removes the Mg(OH)₂ particles as wellas the target particles, and they fall to the floor of the pen and areremoved from the aqueous ecosystem. The larger particles trap a largenumber of smaller suspended particles that cause the turbidity. Theflocculated particles are part of the sludge removed from the pens on aregular basis in many aquaculture practices.

It follows that the first and second aspects are optimised for smallparticles that have a long residence time, while the third and fourthaspects are optimised by larger particles that are sufficiently largethat they pass through the aqueous ecosystems. The control of theparticle size allows for such control.

The aspects considered above are concerned with the health of theaqueous ecosystem. Experiments have shown that the larger particles thatmove into the benthic ecosystem play a significant role in the health ofthat ecosystem, whether or not the particles have sequestered heavymetal ions or have deposited other particles. A sixth aspect isassociated with the benefits of a healthy benthic ecosystem arising fromthe presence of nano-active Mg(OH)₂. It is often observed that thesludge at the base of an untreated aquaculture pen is septic, with acharacteristic small of H₂S, it is acidic and anaerobic. This generallyarises from the anaerobic bacterial decomposition of organic matter,from faeces and uneaten food, as a result of the high population densityof the cultivated species. It is a known art that the dosing of sewagesystems by Mg(OH)₂ is a means of raising the pH to a level that thedecomposition is suppressed. Further, the use of nano-active Mg(OH)₂ maysuppress the growth of pathogenic organisms in this benthic ecosystem,and mitigate their growth such that they do not significantly move intothe aquatic ecosystem and infect the cultivated species. Experimentshave shown that the sludge that is removed from the base of the pond orpen in which the nano-active Mg(OH)₂ has been added has very littlesulphide smell, and is more compact compared to an untreated sludge. Thedegree of compaction is related to the same factors as flocculation, sothat high surface area, and high porosity lead to more compact sludge.The practices in agriculture associated with sludge vary widely. In somecases, the sludge is decomposed in anaerobic digesters to produce afuel, and experiments have shown that the presence of nano-activeMg(OH)₂ decreases the H₂S, and increases the methane content. In onepractice, the sludge is sold as a fertilizer, and the absence of the H₂Sodour is benefit In another practice, the water is drained before beingrefilled and restocked, allowing a time for regeneration of the pond bedin aerobic conditions. The time for regeneration is significantlyreduced if the anaerobic conditions of the sludge have previously beenreduced and the sludge is compact as a result of dosing with nano-activeMg(OH)₂.

A seventh aspect of the invention is the use of the nano-Mg(OH)₂application in aquaculture is as a coating on aquacultureinfrastructure. Experiments have shown the nano-active Mg(OH)₂ minimisesthe formation of biofilms. The result is that secondary growth ofbarnacles is also suppressed. Without being bound by theory, the mode ofaction of the nano-Mg(OH)₂ is believed to arise from the encapsulationof the particles by the extracellular extrusions of biofilm formingorganisms, and the subsequent release of ROS and increase of the pH inthe biofilms degrades the films, and leads to the disruption of thecolonies of the biofilm forming organisms. This aspect is applicable tothe maritime industry, as well as the aquaculture industry. Forshipping, the presence of a biofilm causes a roughness on the hull, andthe higher expenditure of energy. For aquaculture, the biofilm causesdestruction of the pond enclosures, and fouling of equipment used tomanage the cultivation. Depending on the application, the strength ofthe nano-Mg(OH)₂ coating can be enhanced by using additives. Theseinclude acrylic materials used in paints, and other stabilisingmaterials. For example, the use of graphene fibres is particularlyuseful in such applications.

In this specification, the word ‘comprising_ is to be understood in its‘open_ sense, that is, in the sense of ‘including_, and thus not limitedto its ‘closed_ sense, that is the sense of ‘consisting only of_. Acorresponding meaning is to be attributed to the corresponding words‘comprise_, ‘comprised_ and ‘comprises_ where they appear.

While particular embodiments of this invention have been described, itwill be evident to those skilled in the art that the present inventionmay be embodied in other specific forms without departing from theessential characteristics thereof. The present embodiments and examplesare therefore to be considered in all respects as illustrative and notrestrictive, with all changes which come within the meaning and range ofequivalency therefore intended to be embraced therein. It will furtherbe understood that any reference herein to known prior art does not,unless the contrary indication appears, constitute an admission thatsuch prior art is commonly known by those skilled in the art to whichthe invention relates.

In one embodiment of the present invention, there is provided a reactionapparatus for producing biocide powder or a chemical detoxifier powderor a catalyst support from a carbonate mineral, comprising: a firstgrinder for carbonate compounds and a second grinder for hydroxidecompounds; an externally heated counter flow flash calciner thatproduces high surface area oxides from the ground carbonate; anexternally heated counter flow flash calciner that produces high surfacearea oxides from the ground carbonate; and a blender in which thecalcined solid powders are mixed together, and or with other groundsolids for the production of a biocide powder.

In another embodiment the reaction apparatus further comprising ahydration reaction vessel for the production of the slurry producthaving an inlet for the blended powder and a water inlet and a shearingapparatus for shearing the reaction mixture; and a steam outlet forrelease of steam from the reaction vessel, such that in use the reactionis controlled by allowing heat of hydration to raise the temperature ofthe reaction mixture, allowing water to boil off from the reactionmixture as hydration proceeds, and removing steam via the steam outletto remove excess heat and control reaction temperature at boiling pointand a means of quenching the slurry to below 60° C., preferably bytransfer of the slurry to a cooled container and a means of cooling theslurry to ambient temperature; and a means of adding solid or liquidadditives to the slurry.

In a further embodiment, the reaction apparatus is adapted forpost-processing the bioactive power or slurry from the apparatus by oneor more of the following steps:

-   -   sparging the powder or slurry with a gas adjuvent such as ozone        to enhance bioactivity;    -   adding and mixing liquid adjuvent compounds to the powder or        slurry to enhance bioactivity;    -   adding and mixing materials to the powder or slurry to make a        biocidal coating product or    -   adding and mixing materials to the powder or slurry to make a        biocidal emulsion or foam.

In one embodiment of the present invention, there is provided a chemicalcomposition as a powder adapted for use as a biocide, wherein thecomposition comprises: a powder of micron scale calcined particles whichare formed from a mixture of carbonate compounds and hydroxidecompounds, and which have additives to boost the biocide impact such asozone, hydrogen peroxide wherein the particles have a porosity ofgreater than 0.5 and wherein the pore surface is largely composed ofnano-crystalline structures.

The chemical composition as a slurry is adapted for use as a biocide,wherein the composition comprises a slurry produced by hydrating thepowder of mentioned above with additives that stabilise the slurry.

In another embodiment, the chemical composition is presented as acoating material slurry adapted for use as a biocide, wherein thecomposition comprises a coating material produced by mixing the powderor the slurry mentioned above with additives that set the material whenapplied to a surface.

In another embodiment, the chemical composition is presented as a foam,spray or emulsion material slurry adapted for use as a biocide, biofilminhibitor, or plant root repellant, wherein the composition comprises afoam, spray or emulsion material produced by mixing the powder or theslurry mentioned above with additives that form a foam, spray oremulsion when processed.

Although the invention has been described with reference to specificexamples, it will be appreciated by those skilled in the art that theinvention may be embodied in many other forms, in keeping with the broadprinciples and the spirit of the invention described herein.

The present invention and the described preferred embodimentsspecifically include at least one feature that is industrial applicable.

1. A process for producing a biocide powder, comprising the steps of: a.selecting one or more carbonate compounds with a predeterminedcalcium/magnesium ratio; b. grinding the carbonate compounds to producea carbonate powder with a first predetermined particle sizedistribution; c. selecting a magnesium hydroxide compound; d. grindingthe hydroxide compound to produce a hydroxide powder with a secondparticle size distribution; e. calcining the carbonate powder in anexternally heated counterflow flash calciner at a first temperature toproduce a calcined mixture having a surface area sufficiently highenough to exhibit bioactivity; f. calcining the hydroxide powder in anexternally heated counterflow flash calciner at a second temperature toproduce a calcined oxide with a surface area sufficiently high enough toexhibit bioactivity; and g. blending the calcined mixture and thecalcined oxide in a predetermined proportions.
 2. The process of claim 1further comprising the step of adding ground limestone, or lime orhydrated lime to the form the biocide powder.
 3. The process of claim 1,wherein the carbonate compounds comprising Magnesite and Dolomite. 4.The process of claim 3, wherein the degree of calcination of themagnesium carbonate in the magnesite and dolomite is in the vicinity of95% or more, and the degree of calcination of the calcium carbonate isin the vicinity of 5% or less.
 5. The process of claim 1, wherein thecalcined mixture and calcined oxide comprises magnesium oxide (MgO). 6.(canceled)
 7. (canceled)
 8. The process of claim 5, wherein the surfacearea of the oxide from the hydroxide powder is above 200 m²/gm of MgO,and preferably above 250 m²/gm of MgO and most preferably above 300m²/gm of MgO.
 9. (canceled)
 10. (canceled)
 11. (canceled)
 12. (canceled)13. The process of claim 2, wherein the proportion of limestone, lime orhydrated lime depends on the specification to achieve a desirable Ca/Mgratio for the application and to achieve a desirable viscosity andstability of the slurry in conjunction with an amount of carboxylic acidadded in the slurry production process.
 14. (canceled)
 15. (canceled)16. (canceled)
 17. The process of claim 1, further comprising the stepof: a. hydrating the biocide powder with water at or near the boilingpoint of water until the hydration is completed; b. Applying a shearmixing, and c. Adding a carboxylic acid or salt as the thinning agent,in order to form a stable, readily thinned, slurry of the hydrated oxidewith about 60% solids in the final product.
 18. (canceled) 19.(canceled)
 20. (canceled)
 21. (canceled)
 22. (canceled)
 23. (canceled)24. (canceled)
 25. (canceled)
 26. (canceled)
 27. The process of claim13, wherein the carboxylic acid is acetic acid, and the carboxylic saltis magnesium or calcium acetate.
 28. The process of claim 17, whereinthe slurry is mixed with one or more viscosity modifier and settingadditives for manufacturing a coating to sewage pipes and manholes. 29.A reaction apparatus for producing biocide powder or a chemicaldetoxifier powder or a catalyst support from a carbonate mineral,comprising: a. a grinder for carbonate compounds b. a grinder forhydroxide compounds c. an externally heated counter flow flash calcinerthat produces high surface area oxides from the ground carbonate; d. anexternally heated counter flow flash calciner that produces high surfacearea oxides from the ground hydroxide; and e. a blender in which thecalcined solid powders arc mixed together, and or with other groundsolids for the production of a biocide powder.
 30. The reactionapparatus of claim 29, further comprising a hydration reaction vesselfor the production of the slurry product having an inlet for the blendedpowder and a water inlet; and a shearing apparatus for shearing thereaction mixture; and a steam outlet for release of steam from thereaction vessel, such that in use the reaction is controlled by allowingheat of hydration to raise the temperature of the reaction mixture,allowing water to boil off from the reaction mixture as hydrationproceeds, and removing steam via the steam outlet to remove excess heatand control reaction temperature at boiling point; and a means ofquenching the slurry to below 60° C. and a means of cooling the slurryto ambient temperature; and a means of adding solid or liquid additivesto the slurry.
 31. The reaction apparatus of claim 29 further comprisinga second reaction apparatus, wherein the second reaction apparatus isadapted to carrying out one or more steps of: sparging the powder orslurry with a gas adjuvent enhance bioactivity; adding and mixing liquidadjuvent compounds to the powder or slurry to enhance bioactivity;adding and mixing materials to the powder or slurry to make a biocidalcoating product; or adding and mixing materials to the powder or slurryto make a biocidal emulsion or foam.
 32. A chemical composition as apowder adapted for use as a biocide, wherein the composition comprises:a powder of micron scale calcined particles which are formed from amixture of carbonate compounds and hydroxide compounds, and which haveadditives to boost the biocide impact wherein the particles have aporosity of greater than 0.5 and wherein the pore surface is largelycomposed of nano-crystalline structures.
 33. A chemical composition as aslurry adapted for use as a biocide, wherein the composition comprises aslurry produced by hydrating the powder of claim 31 with additives thatstabilise the slurry.
 34. A chemical composition as a coating materialslurry adapted for use as a biocide, wherein the composition comprises acoating material produced by mixing the powder of claim 31 withadditives that set the material when applied to a surface.
 35. Achemical composition as a foam, spray or emulsion material slurryadapted for use as a biocide, biofilm inhibitor, or plant rootrepellant, wherein the composition comprises a foam, spray or emulsionmaterial produced by mixing the powder of claim 31 with additives thatform a foam, spray or emulsion when processed.
 36. The reactionapparatus according to claim 30, wherein the means of quenching theslurry to below 60° C. is by transfer of the slurry to a cooledcontainer.
 37. The reaction apparatus of claim 31, wherein the gasadjuvant is ozone.
 38. The reaction apparatus according to claim 32,wherein the additives to boost the biocide impact is ozone and/orhydrogen peroxide.